1. Field of the Invention
The present invention relates to a controllable electron valve. More particularly, the present invention relates to a multi-electrode electron valve that is able to control, separately or simultaneously, the amount of current, the maximum voltage and/or the effective value of a pulse wave voltage incoming from a power source and outputting to a load. This controllable electron valve combines the large number and impedance of the vacuum tube's command electrodes, the transistor's flexibility, and the thyristor's (SCR's) self-switching mode of operation.
2. Description of Related Art
Conventionally, there exist three controllable electron valves. First, there are vacuum tubes-triodes, tetrodes, pentodes, hexodes, etc. The difference between these vacuum tubes is the number of their command electrodes (grids). Each of the grids (control, screen, suppressor, etc.) allow a vacuum tube to provide increased accuracy for control of the output current. The large impedance of these grids provides a means to control the output current using variations of the input voltage. (The input current is negligible.) This simplifies the vacuum tube's design circuits and allows for exchangeability between the majority of worldwide manufacturers. However, vacuum tubes, with the exception of kinescope tubes, are essentially obsolete, as they are physically large, hot, and fragile and need a high anodic voltage and a separate filament current circuit.
The second type of controllable electron valves are transistors, which have eliminated the disadvantages associated with vacuum tubes. Hybrids such as the Bipolar-MOS-FET are able to work in the linear mode with a large variety of voltages and currents primarily in the low to medium power range. The transistor's use with high power ranges in the linear mode is restricted as its internal dissipation increases. This can be partly overcome by using the transistor in a switching mode, but then sophisticated external circuits are needed to decrease the transistor's transit time and to decrease the noise introduced into the circuit.
Third, there are thyristors (SCRs) which by way of their self-switching operational mode are able to address the dissipation disadvantage of a transistor used with high power. The thyristor's self-switching property is based upon a two transistor positive feedback. See FIG. 1A. When the gate switch is on, a small current I.sub.1 (limited by the resistor) will cross the base emitter junction of the NPN transistor (T2). This current will generate a collector current for the NPN transistor (T2) I.sub.2 =BI1. The second current will generate in the collector circuit of the PNP transistor (T1) a third current, I.sub.3 =BI.sub.2. In this situation the NPN transistor's base current, I.sub.1 becomes larger, I.sub.1 =I.sub.3 =B2I.sub.1. This cycle is repeated infinitely, creating an avalanche, and keeps the entire component in saturation, minimizing the voltage between the thyristor anode and cathode, thereby delivering to the load almost the entire power from the source. The larger internal current, I.sub.3, replaces the small initial current, I.sub.1, and the thyristor maintains itself in the "on" position (self-switching), even if the gate's switch is off The load's resistance will limit, externally, the current according to Ohm's low. A disadvantage of the thyristor-based system is that it requires sophisticated external circuits such as a second SCR or a large power switching transistor, to stop the avalanche when used in a DC power circuit.
The thyristor, at this time, is the ideal controller in high power AC circuits, because the power wave itself decreases to zero. The periodic decrease of the power wave acts as a reset for the thyristor. Each time the power wave reaches zero voltage the avalanche is automatically stopped, and the thyristor will need a new pulse at the gate to begin a new conduction time. However, even in AC circuits, the thyristor requires a sophisticated external circuit to control the power to a load.
A classic thyristor's AC circuit, (see prior art FIG. 1B), utilizes a "zero cross detector" to synchronize a "phase controller" with the positive rectified pulses arising from a rectifier bridge. The "phase controller" acts as a timer from zero to the maximum time of one pulse period. After a predetermined time the "phase controller" will create a means for a UJT driver to provide a short pulse to the thyristor's gate, via a separator transformer. Starting from the gate's pulse moment until the anodic pulse will decay to zero, the thyristor will be an "on" switch, and the load will receive the remainder of the power AC pulse. (See FIG. 5A.)
A disadvantage of the use of an SCR as a power controller is that the stability of the output's effective voltage is affected by the input wave's variations in frequency and/or amplitude. Still another disadvantage of using the thyristor in either AC or DC circuits is the introduction of noise that occurs because there is no internal limitation of the component's current (avalanche). Yet another disadvantage of this component is the way the SCR controls the effective value of a power wave by decreasing the maximum voltage. Loads such as florescent bulbs and some motors do not work efficiently with lower than a nominal voltage.
Therefore, a need exists for a new controllable electron valve that is multi-electrode; has large input impedance; works in a linear, a switching, or a self-switching mode of operation; can integrate the linear and self-switching modes of operation for each power pulse period; introduces relatively low noise; has low internal dissipation; does not rely on sophisticated external circuits for the switching mode; provides for internal limitation of current; and does not necessarily decrease the maximum voltage of the power wave in order to decrease its effective value.